1. Field of the Invention
The present invention relates to the continuous production of multilayer composites which consist of at least two layers of silicone elastomer, the thickness of the individual layers being between 0.1 and 200 μm and the thickness precision is ±5% measured over an area of 200 cm2, and also to the silicone films produced by this method, and to their use.
2. Description of the Related Art
EP1971720B1 describes the production of multilayer composites on a carrier, where at least two layers are applied before crosslinking takes place. The method described has the disadvantage that the required thickness precisions of the individual layers are not achieved.
EP0781198B1 describes multilayer adhesive constructions which in addition to the layer material comprise a barrier layer and also an adhesive layer, in order to minimize the migration of the migratable additive present in the adhesive layer. This method as well does not allow the desired layer thickness to be produced while maintaining thickness precision at the same time.
EP0097313A1 describes the production of a thin film of silicone elastomer, having a film thickness of between one and 500 μm and, during production, being applied to a coated paper. This is done using the coating techniques of roller coating, air doctor or reverse roll coating, wire-wound bar coating or spray coating in order to produce thin films. These techniques lead to films which do not have the required thickness precisions.
DE2408659 describes a method for producing thin, flawless silicone films, in which the film of silicone is produced by casting a centrifuged silicone material to which solvent has been added. The costly and inconvenient method is unsuitable, however, for industrial production in a continuous process. Moreover, the thickness precisions required are not achieved by means of casting processes.
As the prior art shows, silicone films in a thickness range starting from about 200 μm and up to several mm can be produced by extrusion methods or molding methods. The respective methods here exhibit different disadvantages. In the case of discontinuous molding methods, a reduction in the layer thickness is accompanied by problems during automatic demolding, and, moreover, the production costs per square meter (sq. m.) of film are higher than in the case of continuously operating processes. Extrusion methods of HTV rubbers have the disadvantage of relatively large variations in thickness, and also of the limited possibility, owing to plant design and slot swelling, of reducing the layer thicknesses below 200 μm.
In addition to the absolute layer thickness, the uniformity of the layer thickness over the whole of the web produced is a critical factor for applications of the composites in, for example, optical, electrical or medical sectors.
Composites of this kind with thicknesses of the respective individual silicone layer of between one and about 250 μm may be situated in particular in the area of dielectric electroactive polymers (EAP for short), where the silicone layer is used as a dielectric in a flexible, capacitor-like construction. Applications thereof in actuators, sensors, or generators are based on the conversion of electrical energy into mechanical energy or of mechanical energy into electrical energy. Such composites, moreover, have exacting requirements in terms of their mechanical properties, in order to minimize maintenance costs, since they are subject to continual mechanical load.